docs: def generate_custom(self, cpu, vcpu_num, fill_topology):
          """
          Generate custom CPU model. This method attempts to convert the dict to
          XML, as defined by ``xmltodict.unparse`` method.
  
          Args:
              cpu(dict): CPU spec
              vcpu_num(int): number of virtual cpus
              fill_topology(bool): if topology is not defined in ``cpu`` and
                  ``vcpu`` was not set, will add CPU topology to the generated
                  CPU.
  
          Returns:
              lxml.etree.Element: CPU XML node
  
          Raises:
              :exc:`~LagoInitException`: when failed to convert dict to XML
          """
  
          try:
              cpu = utils.dict_to_xml({'cpu': cpu})
          except:
              # TO-DO: print an example here
              raise LagoInitException('conversion of \'cpu\' to XML failed')
  
          if not cpu.xpath('topology') and fill_topology:
              cpu.append(self.generate_topology(vcpu_num))
          return cpu